Field of the Invention
The present invention relates to a wafer processing method for dividing a wafer, which has a plurality of scheduled division lines formed in a grading on a front face thereof and has devices formed in a plurality of regions partitioned by the scheduled division lines, along the scheduled division lines.
Description of the Related Art
In a semiconductor device fabrication process, a plurality of regions are partitioned by scheduled division lines arrayed in a grating on a front face of a semiconductor wafer of a substantially disk shape, and devices such as ICs or LSIs are formed in the partitioned regions. By cutting the semiconductor wafer formed in this manner along the scheduled division lines, the regions in which the devices are formed are separated from each other to fabricate individual device chips.
The cutting of the semiconductor wafer along the scheduled division lines is normally carried out by a cutting apparatus called a dicing saw. The cutting apparatus includes a chuck table for holding a workpiece such as a semiconductor wafer or an optical device wafer thereon, cutting means for cutting the workpiece held on the chuck table, and cutting feeding means for moving the chuck table and the cutting means relative to each other. The cutting means includes a spindle unit which in turn includes a spindle, a cutting blade mounted on the spindle and a motor for driving the spindle to rotate. The cutting blade has a disk-shaped base and an annular cutting edge mounted on an outer periphery of the side face of the base. The cutting edge is fixed to the base by electrocasting of diamond abrasive grain of a particle size of, for example, approximately 3 μm and is formed with a thickness of approximately 20 μm.
However, since the cutting blade has a thickness of approximately 20 μm, it is necessary for the scheduled division lines for partitioning the devices from each other to have a width of approximately 50 μm. Therefore, the cutting apparatus has a problem in that the area ratio of the scheduled division lines occupying in the area of the wafer is high and the productivity is low.
Meanwhile, as a method of dividing a wafer such as a semiconductor water, also a laser processing method called internal processing has been put into practical use in recent years in which a pulse laser beam of a wavelength having a transparency to the wafer is used and irradiated with a focal point thereof positioned in the inside of a region in which the wafer is to be cut. A division method which uses the laser processing method called internal processing is a technology of irradiating a pulse laser beam of a wavelength having a transparency to a wafer from one face side of the wafer with a focal point thereof positioned in the inside of the wafer to continuously form a modified layer along a scheduled division line in the inside of the wafer and applying external force to the wafer along the scheduled division line along which the strength has dropped by the formation of the modified layer to break and divide the wafer (refer to, for example, Japanese Patent Laid-Open No. 2004-160493).
As a method of applying external force along a scheduled division line of a wafer along which a modified layer is formed to divide the wafer into individual device chips, a technology is disclosed in Japanese Patent Laid-Open No. 2005-223282. According to the technology, a wafer having a modified layer along scheduled division lines is adhered to a dicing tape mounted on an annular frame, and the dicing tape is expanded to apply tensile force to the wafer to divide the wafer so as to separate individual device chips from each other along the scheduled division lines along which the modified layer is formed and the strength is dropped thereby.
Another technology is disclosed in Japanese Patent Laid-Open No. 2013-165229. According to the technology, a protective tape is adhered to a front face of a wafer in which a modified layer is formed continuously along scheduled division lines and the wafer is held at the protective tape side thereof on a chuck table. Thereafter, the wafer is ground on the back face side thereof while grinding water is supplied thereto to form the wafer so as to have a predetermined thickness and the wafer is divided into individual device chips.